Relay satellite broadcast system



NOV. 21, 1950 W- DARLlNG 2,531,199

RELAY SATELLITE BROADCAST SYSTEM Filed March 25, 1947 .lY/I-U JNVENTJOR.

Patented Nov. 21,` 1950 STATES PATENT former' RELAYfsArnLnrgsncnsr SYSTEM Woodrow Darling, 'Merchantville, N. --J., .assigner to lRadio Corporation of Amer-ica., a corporation of .Delaware Application March'25, 1947, l Serial No. '7375031 Cl. Z50-6) A n 4 fClaims.

This `annlication'discloses an improved broadcasting system land .has .as its k:rn-ain 3,object provision of :a simplified 'satellite broadcast .system wherein 'the main 'statioln is connected to the auxiliaryicr -boos'terfstation by a radio .re-lay. 'The iouzifster for satellite fstation is arranged to cover -lan area not well serviced bythe main station .zand bot-h 'transmitting stations iopera'te on fthe saine frequency.

Heretotore, separate translnitting vsystems have lbeen fused in Ethe main station :and fat' the satellite for ibooster station .a `cormnovn :audio supply Vtor separate Asrnodulator `.circuits at the separate transmitter. IIn futher `Words, 1in these systems, `tuvo substantially complete .exciters yand transmit .fters :are 'used with fthe audio 'or modulation fcir 'cuits .being .the only :circuits :common to both fstations. y 1

A more 'detailed fobject of my invention :is to provide essentially a single transmitter l:system much rproduces .the signal to 'fbe ibroadcast :at the main station and :also the rsifg-n'al to `'bie telen/red Vto the :secondary `broadcast ,or satellite fstation.

Furthermore, the relayed signal 'is to be llocked Yby the broadcast `sig-nal at the chain 'station and is used as `emzi'tation yfor the transmitter at 'the .secondary station so that AAiin feffect, the two :signals which fare broadcast :are locked in synchron-ism leach with fthe other.

ln systems of this' nature, the FCC, of "course, assigns the main 'broadcast transmitter frequency fof operation `and -aflso a band of frequencies wherein the relay-ing is `to take place.

-A-furtherfobject of my vinvention is :to provide a isimplified 'satellite system wherein although the broadcast :frequency is fixed, the frequency `at which 'relaying may be married out is readily changeable lin 4:small `steps V.to :suit the conditions atrhand.

Briely, vtheseo'm'ects'a-re attained inlaccordance with :my invention by usi-ng, if at hand, lor pro- `aiding, if not at fnand, a frequency modulated Icarrier such as commonly -used for exciting, through multipliers,transmitters `which -m'ay be ,-i-n existence r.or 'may be provided. Carrier .energy -is liver-ted@from the exciter and modulated signal .from the main transmitter., operating -at a multi- .plied i11equenc,rand ,un-ined The .sum side band is selected and .multi-plied to -the .frequency lat ,WhiGhrelaying -is-.to vtaire place and transmitted,

.modulationforboth. Prior to relayingfby radiation, the frequency multiplied frequency modulated carrier is modulated in amplitude by the exciter carrier.' The amplitude modulation :may 'be small, -say A115% Ito `20% which lwill be :sufficient :for yselection of the'exciter carrier 'at the satellite .or booster station. At the booster 'station-the received :relayed signa-l is 4divided r-down and #de- -tected to 'derive fthe amplitude 'modulation which represents the 'exciter carrier. This carrier is then inixedwiththemain'signal after it is further divided, if 'necessary, and fthe frequency "modu- Ylated difference frequency 'talk'en for the :booster transmitter. The frequencies *involved are selected so that the `booster :transmitter frequency 'andthe main-transmitter requency'are :the same and as assigned foruseat the station.

There 4has been some tendency 'to goto vhigher frequencies ffor radio relaying. This :creates 'difculties 'in the use of conventional a.tubes .and circuits. I

AA further :object fof the `present invention iis 1to provide 1simplified satellite system lwhenein the 'rela-ying `takes place `at'frequencies low enough .to =be efciently handled by v,tubes fof .the lighthouse type. Then `:a system arranged Iin 4laccordance with my invention may be used without design fdiiculties..

In describing any invention in Ydetail, Yreference :will be made :to the attached drawings wherein Fig. 1 Yillustrates -a relay-satellite broadcast system y 4a'iurarurced zin accordance vwith im-y invention, while Fig. I2 'illustra-tes -one form -of rectier and tfre'- fq-uency divider which may tbe 'used int-he -fre `quencydividing 'circuits -of -my system.

In' 1., -2 isa Wavelength :modulation system ,using the term asde-ned above. :In thedescri-p- -tion which follows, -the Ysaine has been freferredto fasza frequency modulation System. It may befc'f various types such as, 'for example, `a lcorrected phase modulation system with -Inultilo'liers or 'a 'direct frequency modulation system or it r'n'ay be :a frequenc'ymodula'ton V'sys'tenl l'ofthe type using 4a 'frequency inodulated oscillator, and 'la fixed oscillator with means *for selecting Vvfor 'usel'a'bealt .frequency resulting from inixin'g the modulated 4oscillations andthe oscillations of xed frequency. At L'Ihave shown a source o oscillations of Xed fflllncy which may be as. supplied as carrier 'energy 'to .the apparatus in 2 'including 'the modulation `source .and fmodulator. The frequency v.modulated output .is .supplied .to amplifiers and .frequency multipliers .in .unit Sand then used .to excite the .main transmitter .8. 'llhe'transrnltter .3

g includes `.the v.usual amplifiers. The modulated oscillations as increased in amplitude and frequency are broadcast.

The source 4 is of substantially fixed frequency and may comprise a stabilized wave generator with multipliers, for example, a crystal oscillator and if desired, multipliers. A source stabilized in frequency by automatic control means may also be used here. oscillations from the source 4 are supplied to a mixer 6 and to an amplitude modulator I4. In the mixer 6, the oscillations of substantially xed frequency are mixed with modulated oscillations from the main transmitter and a side band is selected by unit I0. The side band selector in IIJ may comprise sharply tuned circuits and the output thereof, which is a frequency modulated wave, is supplied to a frequency modulated and amplitude modulated wave relay transmitter I2. The carrier wave from source 4 is also supplied to the amplitude modulator I`4 and used thereby to modulate the amplitude of the frequency modulated wave supplied at I2. A small amount of amplitude modulation only is required here, for example, to 20 per cent. The wave in I2 is multipled the desired amount to bring it up to the relay frequency band and the same is relayed by parabolic antenna I6. The relayed wave is intercepted and reduced in frequency in unit by division. Two outputs are taken from the frequency divider in 20. One goes to further frequency dividers in 22 and the other is passed to an amplitude modulation detector in 24 wherein the modulation components resulting from amplitude modulation of the frequency modulated and multiplier carrier by the oscillations of fixed frequency from source 4 are demodulated and selected to be supplied to a mixer 26. The mixer 26 is also supplied with output from the divider 22. The frequency selected is such that a side band selected from the output of the mixer 26, is of the same frequency as the frequency modulated wave transmitted from the main transmitter at 8. This selected side band goes to the booster transmitter 28 which may comprise amplifiers as desired and is radiated to service an area not well reached by the transmitter 8.

In my schematic diagram, I have not shown the amplifiers as separate units. It will be understood, of course, that amplification takes place where needed and the amplifiers may be conventional. For example, the units 3 and 8, in addition to including the necessary frequency multipliers, will include the necessary amplifiers. The mixer in 6 may be a conventional simple demodulator. The selectors in unit I0 may be tuned circuits and may include amplifying stages if desired. This unit and/or the unit I2 may include the necessary frequency multipliers. The unit I2 may include a stage wherein modulation takes place in a conventional manner under control of the output of the amplitude modulator I4. The divider 2D at the satellite station may include or be preceded by an amplifier. Amplifiers may be included in unit 22 and in the output of the mixer 26 and in the unit 28.

Although I do not limit my system to the use of any particular frequencies for broadcasting or for relaying, examples of the frequencies which may be used, will be given. In selecting these frequencies, I have kept in mind frequencies which have been assigned by the FCC for frequency modulation broadcast channels and for relaying purposes. The source in 4 might have an output of 4.4 megacycles and the main transmitter 8 might operate at 88 megacycles. Then the unit 3 and/or 8 includes multipliers having a multiplication factor of 20. The upper side band might be selected from the output of 6 and then is 92.4 megacycles. Then the multipliers in I2 may have a multiplication factor of 10 and the dividers in units 20 and 22, a total factor of division equal to l0. This gives an input to the mixer 26 from the divider 22 of 92.4 megacycles so that the lower side band selected from the output at 26 is at 88 mc.

Although, in general, the broadcast frequency once assigned is not changed, sometimes permission to change the relay frequencies is obtain- -able and provision is made in my system for changing the same. For example, the output of oscillator 4 might be doubled in frequency in which case, the mixer 6 would have an output of 96.8 mc. and relaying radiation might take place at 968 mc. At the satellite station, the same process described hereinbefore would be used.

An advantage of my system is that the frequencies used are such that good efficiency can be obtained by use of known tubes, and an antenna of parabolic type works very well.

As to the transmission, there is no audio phase shift because the circuits used are suiiiciently broad to treat all frequency modulation side bands uniformly so that they retain the original audio amplitude and phase in the booster transmitter. Other systems that use separate frequency controls at the separate transmitter, introduce audio phase shift and set up audio beats which permit passage of noise through the listener sets in certain areas of overlap of essentially equal signal strength. In my system, there will be no region wherein the signals will produce low frequency beats, because they are synchronized. Another advantage of my system resides in the elimination of frequency discriminators and other circuits of the like critical nature, wherein tuning and balance is diiiicult and wherein phase shift and dissimilarities may be produced. Moreover, in my system, remodulation of a carrier by the signal in the booster is not necessary.

As stated above, the frequency dividers in units 2G and 22 may be conventional and may be separate from the detector in unit 24. However, in Fig. 2, I have shown an improved frequency divider and rectifier for use at 20 in my system. Then the amplitude modulation detector in 24 is omitted and the divided output of unit 20 is fed to unit 22 and the rectified output of unit 20 is fed to the mixer 26. This divider is shown in Fig. 2 as being connected directly to a parabolic antenna, but it may be coupled thereto by amplifiers. The divider and rectifier comprises a discharge tube 3U with its grid connected to a parallel tuned circuit 32 tuned to the relayed signal frequency. The circuit includes a grid leak and condenser unit GR. The anode is coupled in a parallel circuit 34 tuned to one-half the frequency of circuit 32. The anode is also coupled with a second parallel circuit 35 tuned to the frequency Fo of the carrier used to amplitude modulate the frequency modulated signal in the unit I2. The condenser 31 is a bypass for voltage of the divided frequency while the condenser 39 is a plate source bypass condenser. Output at the divided frequency may be taken by an inductance 4I coupled to the inductance of circuit 34. The rectified components of frequency F0 appear across circuit 35 and may be fed by coupling inductance 43 to the mixer 26. Regeneration is used, being obtained by coupling inductance 36.

The time constant of the grid leak condenser combination is adjusted so that its time constant is long compared with 1000 mc. and short compared with 4.4 mc.

During operation, an excitation positive peak on the grid of tube 30 overcomes the negative bias and causes the tube to amplify to excite the plate circuit 34 to develop oscillations at a fraction of the excitation frequency. Feed back takes place at the divided frequency and when the voltages fed back and the original excitation voltages are positive at the same time the bias is overcome and the plate circuit is again excited to set up oscillations of the divided frequency. When the system is adjusted to divide by two, a positive excitation peak occurs when the feed back would be positive, and this starts oscillations inthe circuit 34. The next positive excitation peak (peak number two) is ineffective because the feed back voltage is negative but the third positive peak is again effective since it occurs when the second positive peak of the divided frequency occurs.. In other words, regeneration takes place on every other positive peak of the applied wave. Rectification takes place and the amplitude modulations of frequency Fo are set up in circuit 35.

What is claimed is:

1. In a satellite broadcast system, a main transmitter, a secondary transmitter at a distance therefrom operating at the same frequency at which the main transmitter operates, a source of excitation for the main transmitter comprising a carrier modulator and a frequency multiplier and a source of excitation for said secondary transmitter which synchronizes it with said main transmitter comprising means for combining wave energy representing the multiplied modulated carrier with wave energy representing the carrier and for selecting a side band resulting from said combination, means for multiplying the frequency of the selected side band and modulating it in accordance with wave energy representing said carrier, means for relaying the resultant energy to said secondary transmitter, means for frequency dividing and detecting the relayed energy to derive wave energy representing said first mentioned carrier, and means for mixing said derived energy with the energy of divided frequency to obtain excitation energy for the secondary transmitter.

2. In a satellite broadcast system, a main transmitter, a secondary transmitter at a distance therefrom operating at the same frequency at which the main transmitter operates, a source of excitation for the main transmitter comprising a frequency modulator for a carrier and a frequency multiplier and a source of excitation for said secondary transmitter which synchronizes it with said main transmitter comprising' means for combining wave energy representing the multiplied frequency modulated carrier with Wave energy representing the carrier and for selecting a frequency modulated side band resulting from said combination, means for multiplying the frequency of the selected frequency modulated side band and modulating its amplitude in accordance with wave energy representing said carrier, means for relaying the resultant energy to said secondary transmitter, means for frequency dividing and detecting the amplitude modulated relayed energy to derive wave energy representing said first mentioned carrier, and means for mixing said derived energy with the energy of divided frequency to obtain excitation energy for the secondary transmitter.

3. In a satellite broadcast system, a main transmitter, a secondary transmitter at a distance therefrom operating at the frequency at which said main transmitter operates, means for exciting the main transmitter comprising a single substantially constant frequency source of carrier energy modulated in accordance with signals with frequency multiplying means coupling said source to said main transmitter, means for transmitting to said secondary transmitter oscillatory energy representing said carrier and multiplied modulated carrier, a mixel1 excited by said oscillatory energy and by oscillatory energy of the carrier frequency, and means for using a sideband frequency at the output of said mixer for exciting said secondary transmitter.

4. In a satellite broadcast system, a main transmitter, a secondary transmitter at a distance therefrom operating at the frequency at which said main transmitter operates, means for exciting the main transmitter comprising a single substantially constant frequency source of carrier energy modulated in accordance with signals with frequency multiplying means coupling said source to said main transmitter, and a source of excitation for the secondary transmitter comprising a mixer excited by carrier energy from said firstnamed source and by multiplied modulated carrier, a frequency multiplier coupled to the output of said mixer, a modulator for the multiplied mixer output energy, said modulator being excited by carrier energy from said first-named source, and means for relaying the modulated multiplied mixer output energy to said secondary transmitter.

WOODROW DARLING.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,754,881 Clement Apr. 15, 1930 2,094,113 Affel Sept. 28, 1937 2,127,015 Tillyer Aug. 16, 1938 2,140,730 Batchelor Dec. 20, 1938 2,186,130 Wintringham Jan. 9, 1940 2,248,797 Waller July 8, 1941 2,292,222 Haigis Aug. 4, 1942 2,397,913 Bernstein Apr. 9, 1946 2,399,469 Cook Apr. 30, 1946 2,421,727 Thompson June 3, 1947 2,458,124 Wilmotte Jan. 4, 1949 OTHER REFERENCES FM and Television, December 1944, Co-Channel Synchronous FM Satellite, pages 18-21 and 75, by Phil B. Laeser. 

